To manufacture pile fabrics, like velvet and plush fabrics, weaving machines are primarily used, which simultaneously weave two fabric strands one above the other, between which are arranged the pile threads which are to be separated at the end of the weaving process. In order for the pile to have the desired quality, a fine control over the heddle frame, particularly at the end positions of the pile heddle frames, must be performed. The heddle frames move thereby between three shed positions, namely, a lower shed position, a middle shed position and an upper shed position. The center shed, and the type and manner with which the heddle frame moves through it, is of a very special importance. The middle-shed positions of various heddle frames overlap or undercut one another in special cases.
U.S. Pat. No. 3,759,298 describes in greater detail the theoretical and practical mode of operation of a machine for the manufacture of such a fabric. Various types of drives for the pile heddle frames are discussed. These can be identified as addition gearings, since two elements which are each driven by a baulk are coupled with one another in such a manner that they reciprocally influence their attained positions. The movements which are achieved with the drives are transmitted through long rods in the heddle frame actuating mechanism onto the heddle frames. In a more compact construction of the weaving machine having a dobby, the long rod of the heddle frame actuating mechanism becomes considerably shorter, from which result distortions in movement. Furthermore, undesired changes in the two end positions of the pile heddle frame were found, when the position of the heddle frame is controlled in the area of the center-shed position.
The purpose of the invention is to eliminate the unfavorable influence of a particularly short connecting rod and to simplify the adjusting operations for the three basic positions.
This is achieved in the mentioned heddle frame actuating mechanism by arranging in the heddle frame actuating mechanism between one arm on each of two pivotal double arm levers a relatively short connecting rod so that in the center position of the heddle frame, the arms form with the connecting rod and a connecting straight line extending between two basic pivot axles of the arms a parallelogram. This is practically achieved in the linkage connection by inventively providing the heddle frame actuating mechanism with a relatively short connecting rod, one end of which is hingedly movable and securable on the second arm of the second double arm lever, and the second end of the connecting rod is hingedly connected to the first arm of a third double arm lever of the heddle frame actuating mechanism, which is supported on a fixed axle. In the shed-center position of the heddle frame, the second arm of the first double arm lever extends in alignment, namely a rectilinear extension of the second arm of the second double arm lever and the two arms together are equal in length up to the hinge point of the connecting rod in the phase of the center position, as the length of the first arm of the third double arm lever, and form a parallelogram with the connecting rod and a connecting line extending through the pivot axles supporting the first double arm lever and the third double arm lever which makes it possible in this position to move the connecting rod parallel and to hinge same again on the adjacent arms without changing the heddle frame position.